The basic architectural concept in MPEG-21 is the Digital Item. Digital Items are structured digital objects, including a standard representation and identification, and metadata. They are the basic unit of transaction in the MPEG-21 framework. Many MPEG-21 applications have the requirement to uniquely identify Digital Items.
ISO/IEC 21000-3:2003 provides a simple but flexible mechanism to:
The DII specification does not specify new identification systems for the content elements for which identification and description schemes already exist and are in use.
Identifiers covered by this specification can be associated with Digital Items by including them in a specific place in the Digital Item Declaration (ISO/IEC 21000-2).